Panopticlick

Generates temporary disposable email address, to avoid giving your real details.

Show how identifiable you are on the Internet by generating a fingerprint based on device information. This is how many websites track you (even without cookies enabled), so the aim is to not be unique.

Checks if a given website is blocked by filters applied by your mobile and broadband Internet Service Providers (ISP).

Shows which of personal identity data is being leaked through your browser, so you can better protect yourself against fingerprinting.

Displays, and removes Meta and EXIF data from an uploaded photo or document.

Scan websites and shows a security overview, relating to factors such as HTTPS, domain info, email data, www protocols and so on.

Checks if your credentials (Email address or Password) have been compromised in a data breach. See also Firefox Monitor.

Shows your IP address, and other associated details (location, ISP, WebRTC check, DNS, and lots more).

Checks if a website or business is a scam, before buying something from it.

Tool for analyzing email headers, useful for checking the authenticity of messages, as well as knowing what info you are revealing in your outbound messages.

Analyzes emails, checking the URLs and creating a SHA256 and MD5 hash of attachments, with a link to VirusTotal. To use the service, just forward a potentially malicious or suspicious email to [email protected], and an automated reply will include the results. They claim that all email data is purged after analysis, but it would be wise to not include any sensitive information, and to use a forwarding address.

Check where a suspicious URL redirects to (without having to click it). Lets you avoid being tracked by not being redirected via adware/tracking sites, or see if a shortened link actually resolves a legitimate site, or see if link is an affiliate ad.

Ever been uninstalling programs from your Windows PC and been unsure of what something is? Should I Remove It is a database of Windows software, detailing whether it is essential, harmless or dangerous.

A tool from Netcraft, for analysing what any given website is running, where it's located and information about its host, registrar, IP and SSL certificates.

Analyses a potentially-suspicious web resources (by URL, IP, domain or file hash) to detect types of malware (note: files are scanned publicly).

Checks how many, and which trackers any Android app has. Useful to understand how data is being collected before you install a certain APK, it also shows which permissions the app asks for.